In conducting the measurement of EMG signals, electrodes are placed or adhered onto the skin, usually with a layer of electrically conducting gel between the skin surface and the electrode proper. The quality of the signals received will depend on the quality of the connection made between the skin and the electrode, and this may not be easy for the user to ascertain. If the connection is poor, the sensing of particular signals may fail and actions that should be triggered in response to particular conditions may not take place. In Functional Electrical Stimulation systems, electric currents are impressed on the skin by voltage applied via skin electrodes either to produce a muscular reaction or to provide a sensory input. If the connection between the electrode and the skin is poor, this can lead to excessive voltage being applied or can lead to a failure to produce the desired effect.
For instance, in WO2004/087258, episodes of bruxism are detected by monitoring EMG signals received from electrodes on the skin of a user and when such an episode is detected, an mild electric shock is applied via the electrodes as a biofeedback signal. In order that the apparatus can function correctly to detect the bruxism episodes and also to apply the biofeedback signal safely, a good connection between the skin and the electrodes is required. It is described that the connection can be checked by applying a voltage between a pair of the electrodes to be tested, so as to produce a predetermined current, and measuring the voltage required, and further that the user is informed, in case of reduced connection, to adjust the apparatus, such as the strap pressing the electrodes to the skin.
All patent and non-patent references cited in the application, or in the present application, are also hereby incorporated by reference in their entirety.